Reconciling the effects of mutual visibility on gesturing

Fourteen visibility experiments, which compared the overall rate of gesturing when participants could or could not see each other, have produced perfectly contradictory results: Seven found a significantly higher overall gesture rate in the visible condition, and seven found no significant difference. Experiments that used quasi-dialogues in which the addressees’ responses were experimentally constrained (e.g., using a confederate) found a significant difference; the experiments that used free dialogues did not. This review examined three possible explanations and found that (1) the use of quasi-dialogues did not ensure better experimental control, (2) the constrained addressees may have introduced a confound that could account for the significant difference, and (3) although mutual visibility did not affect the overall gesture rate in free dialogues, it significantly increased more specific features of gestures that are useful to addressees. These findings raise several issues about the utility of conventional visibility designs for understanding conversational gestures.